Fix tensorflow include dir

upstream ffmpeg excects[1] : /usr/include/tensorflow/
tensorflow package ships[2]: /usr/include/tensorflow/tensorflow/

References
----------
[1] https://git.videolan.org/?p=ffmpeg.git;a=blob;f=configure;h=a9644e211bebb342fb9066190f1be70e55f68ec0;hb=4154f8967820ca734a77ce91bb590cd77649dee8#l6138
[2] https://git.archlinux.org/svntogit/community.git/commit/trunk?h=packages/tensorflow&id=d6b6fa4eb56d8e6055268504d6b0110c6fddde7e

PKGBUILD

@@ -4,7 +4,7 @@
 pkgname=ffmpeg-full
 _srcname=ffmpeg
 pkgver=4.1.3
-pkgrel=1
+pkgrel=2
 pkgdesc='Complete solution to record, convert and stream audio and video (all possible features including nvenc, qsv and libfdk-aac)'
 arch=('i686' 'x86_64')
 url='https://www.ffmpeg.org/'
@@ -74,10 +74,15 @@ build() {
         # on systems with legacy nvidia drivers
         if pacman -Qs '^nvidia-340xx-utils' >/dev/null 2>&1
         then
-            _ldflags="${_ldflags} -L/usr/lib/nvidia"
+            _ldflags+=' -L/usr/lib/nvidia'
         fi
     fi
     
+    # fix tensorflow include dir
+    ## upstream ffmpeg excects : /usr/include/tensorflow/
+    ## tensorflow package ships: /usr/include/tensorflow/tensorflow/
+    _cflags+=' -I/usr/include/tensorflow'
+    
     printf '%s\n' '  -> Running ffmpeg configure script...'
     
     ./configure \